refactor(proxy): 完成 HTTP adapter cutover (#264)

[g1331]

Summary

完成代理 HTTP adapter 到统一代理请求生命周期 module 的 cutover，删除旧的重复 orchestration 与终态副作用路径。

Related Issue

Closes #264

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Refactoring (code improvement without changing functionality)
• Tests (adding or updating tests)
• Build/CI (changes to build system or CI configuration)

Changes

• 统一 GET、POST、PUT、DELETE、PATCH 到 executeProxyRequest。
• 将鉴权、准入、路由、故障转移与终态副作用保留在生命周期 module 中；HTTP route 仅负责路径参数适配。
• 非流式请求统一通过 settleNonStreamRequest 收口。
• 流开始前失败统一通过 settleStreamFailureRequest 收口，保留 failover history、routing decision、实际上游和 billing attribution。
• 集中流式失败 fixture metadata 构建，避免重复 recording 逻辑。
• 新增 HTTP adapter 回归测试，并更新代理生命周期、故障转移和录制文档。

Test Plan

• Local tests pass (pnpm test:run)
• Type check passes (pnpm exec tsc --noEmit)
• Lint passes (pnpm lint)
• Manual testing completed

Additional verification: pnpm format:check, pnpm build, and pnpm docs:build passed. The full Vitest suite passed with 3600 tests passed and 1 skipped.

Checklist

• Code follows the project's coding standards
• Tests have been added where necessary
• Documentation has been updated (if applicable)
• Changes do not introduce security vulnerabilities
• Commit messages follow conventions

Screenshots

Not applicable; no UI changes.

Additional Notes

The production build and documentation build completed successfully. Existing Turbopack/VitePress warnings did not block either build.